title: Adsorption and dissociation of NH3 on clean and hydroxylated TiO2 rutile (110) surfaces: a computational study.
abstract: The adsorption and dissociation of NH(3) on the clean and hydroxylated TiO(2) rutile (110) surfaces have been investigated by the first-principles calculations. The monodentate adsorbates such as H(3)N-Ti(a), H(2)N-Ti(a), N-Ti(a), H(2)N-O(a), HN-O(a), N-O(a) and H-O(a), as well as the bidentate adsorbate, Ti-N-Ti(a) can be formed on the clean surface. It is found that the hydroxyl group enhances the adsorption of certain adsorbates on the five-fold-coordinated Ti atoms (5c-Ti), namely H(2)N-Ti(a), HN-Ti(a), N-Ti(a) and Ti-N-Ti(a). In addition, the adsorption energy increases as the number of hydroxyl groups increases. On the contrary, the opposite effect is found for those on the two-fold-coordinated O atoms (2c-O). The enhanced adsorption of NH(x) (x = 1-2) on the 5c-Ti is due to the large electronegativity of the OH group, increasing the acidity of the Ti center. This also contributes to diminish the adsorption of NH(x) (x = 1-2) on the two-fold-coordinated O atoms (2c-O) decreasing its basicity. According to potential energy profile, the NH(3) dissociation on the TiO(2) surface is endothermic and the hydroxyl group is found to lower the energetics of H(2)N-Ti(a)+H-O(a) and HN-Ti(a)+2{H-O(a)}, but slightly raise the energetic of Ti-N-Ti(a)+3{H-O(a)} compare to those on the clean surface. However, the dissociation of NH(3) is found to occur on the hydroxylated surface with an overall endothermic by 31.8 kcal/mol and requires a barrier of 37.5 kcal/mol. A comparison of NH(3) on anatase surface has been discussed. The detailed electronic analysis is also carried out to gain insights into the interaction nature between adsorbate and surface.
authors.affiliation: National Center for High-Performance Computing, No. 28, Nan-Ke 3rd Rd., Hsin-Shi, Tainan, 744, Taiwan. changjg@nchc.org.tw
authors.forename: Jee-Gong
authors.initials: JG
authors.lastname: Chang
authors.forename: Hsin-Tsung
authors.initials: HT
authors.lastname: Chen
authors.forename: Shin-Pon
authors.initials: SP
authors.lastname: Ju
authors.forename: Ching-Sheng
authors.initials: CS
authors.lastname: Chang
authors.forename: Meng-Hsiung
authors.initials: MH
authors.lastname: Weng
mesh_terms: D000327:Adsorption; D000641:Ammonia / Q000737:chemistry*; D011789:Quantum Theory; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: C009495:titanium dioxide; D000641:Ammonia; D014025:Titanium